The purpose of this project is to test and refine a hydraulic adaptable ankle-foot system designed to adapt to different terrain on every step of walking. We propose to conduct bench testing and human subjects testing at the Minneapolis VA Health Care System to provide feedback to a collaborative group. Our collaborators are already funded for their part of the project. Three veterans having unilateral transtibial amputation will be recruited to test the adaptable ankle-foot system over the two year period. Testing will include full gait analyses in a motion laboratory to establish the system's ability to maintain consistent function on each of five surface slopes. Additionally, subjects will walk over changing terrain (up and down a free-standing ramp) while the iPecs and motion analysis system collect data needed to examine the ankle torque versus ankle angle characteristics. We hypothesize that the torque versus angle relationship will maintain a similar slope, but will shift toward dorsiflexion for uphill walking ad toward plantarflexion for downhill walking for successfully adapting components. The adaptations are expected to occur on the first step on a new surface. We will also examine the ankle flexion curve, particularly the time needed for the ankle to return to neutral or slightly dorsiflexed position in early swing phase. Subjects will repeat all tests with a non-adaptable ankle-foot system as a control condition. We do not expect to see shifts in the ankle torque versus ankle angle curves for the non-adaptable ankle-foot systems. Findings of bench testing and human subjects testing will be used to suggest areas of improvement for future prototypes. Our group will also assist in changes to the design and manufacturing of new prototypes. If we are able to develop a useful prototype early in this project period, we will begin planning fatigue testing of the ankle-foot system, long term patient testing, and technology transfer to a prosthetics company. PUBLIC HEALTH RELEVANCE: This pilot project is directly applicable to the VA Patient Care Mission in that it will test and improve a hydraulic ankle-foot system designed to adapt to different terrain on every step of walking. Most prosthetic feet are aligned for use on level terrain and do not adapt to different slopes, causing instabilities and discomfort to their users when walking on these slopes. The few systems that do claim to adapt are expensive and slow to adapt or do not have mechanical properties that change for different slopes. The proposed device will adapt without motors or batteries, potentially providing more confidence to the user when walking on varying terrain compared with non-adaptable systems, increasing their engagement in social activities and improving their quality of life.